1. Field of the Invention
The present invention relates to a charging device and an image forming apparatus using the charging device.
2. Discussion of the Related Art
In an electrophotographic image forming apparatus, an image is formed by the processes of uniformly charging a latent image bearing member such as a photosensitive element with a charging device; irradiating the latent image bearing member with light to form a latent electrostatic image thereon; attaching toner to the latent electrostatic image to form a toner image; and transferring the toner image onto a recording medium, for example, a transfer sheet, directly from the latent image bearing member or via an intermediate transfer unit.
As the charging device for use in the image forming apparatus, there is known a charging device that uniformly charges the latent image bearing member by applying a charge bias to a charging member, for example, a charging roller, a charging brush roller, etc., that contacts the latent image bearing member to cause a discharge between the charging member and the latent image bearing member.
However, with such a charging device, reversely charged toner present in residual toner remaining after transfer accumulates on the charging member, which causes deterioration of image quality. Specifically, after a transfer process in which a toner image is transferred onto the intermediate transfer unit or the recording medium, a small amount of toner remains on the surface of the latent image bearing member. This residual toner contains a relatively large amount of reversely charged toner. The reversely charged toner is transferred to the charging member that contacts the surface of the latent image bearing member and accumulates thereon. This accumulation prevents uniform charging of the latent image bearing member, which causes deterioration of image quality. This problem is particularly acute in an image forming apparatus employing a cleaner-less system instead of a cleaning unit that mechanically scrapes residual toner from a latent image bearing member, because in the cleaner-less system residual toner is electrostatically collected into a development unit and therefore a large amount of residual toner contacts the charging member.